Pharmacologic approaches for treating cancer have traditionally relied on the use of various single agent systemic therapies (monotherapies). An archetypical example is chemotherapy, which utilizes broadly cytotoxic drugs that target rapidly dividing cells, including alkylating agents like dacarbazine (DTIC) or temozolomide (TMZ), or mitotic inhibitors like paclitaxel, to inhibit or kill the rapidly growing cells typical of cancer. Tumors may not be completely responsive to such monotherapy, either due to their high collateral systemic toxicity necessitating lower, even sub-therapeutic doses or development of tumor resistance that circumvents the activity of the monotherapy agent. More advanced chemotherapy strategies have been developed that are predicated on use of multiple agents in a combination therapy that simultaneously attack the tumor along multiple of biochemical pathways. Many of these regimens, such as the combination of doxorubicin, bleomycin, viblastine and DTIC for Hodgkin's lymphoma, have been developed through empirical testing. Because of the inherent limitations of their individual pharmacologic components, such approaches remain relatively non-specific with high morbidity, allowing considerable room for improvement in terms of efficacy and safety.
Targeting cancers based on their selective overexpression of certain cell-surface receptors or reliance on specific signaling or metabolic pathways, in particular aberrant pathways present in certain cancers, provides another point of attack. For instance, it has been found that some cancers harbor mutations in certain protein kinases, such as those encoded by the serine/threonine-protein kinase B-Raf gene (BRAF), that are involved in cell signaling and hyperproliferative growth, thereby serving an oncogene role. Targeting these pathways through the use of inhibitors has proven attractive, at least initially, in controlling cancers by staving off the oncolytic signaling. A similar approach based on targeting overexpression of certain receptors, such as epidermal growth factor receptor (EGFR) or vascular endothelial growth factor (VEGF), provides the basis for damping the oncolytic activity of these receptors, for instance by use of antibodies to the targeted receptors (or by use of agents that inhibit the signaling stimulated by these receptors). Unfortunately, as in the case of conventional chemotherapy, these receptors and pathways may play important physiologic roles peripheral to the tumor, leading to toxicity upon their targeting, while the targeted cells also may develop resistance by harnessing alternate biochemical processes or proliferating via selection of resistant clonal subpopulations of tumor cells. Thus, the challenges posed by these types of targeted therapies are substantially similar to those posed by conventional chemotherapy.
In a growing number of oncology indications it is now clear that cancerous tumors employ various methods to evade detection as aberrant tissue and to reduce immune system competency, thereby avoiding potential identification and destruction by the patient's immune system. As a consequence, a number of approaches have been developed to enhance the capability of the patient's immune system to detect and destroy cancers. For example, the anti-CTLA-4 (cytotoxic T lymphocyte-associated antigen 4) antibodies ipilimumab and tremelimumab are designed to counter downregulation of the immune system by blocking CTLA-4 activity and thus augmenting T-cell response against cancer. Alternate approaches may utilize agents that stimulate certain components of the immune system (i.e., upregulation), including administering non-specific cytokines (such as interleukin 1, 2, or 6, “IL-1”, “IL-2” or “IL-6”; interferon-alpha or gamma, “IFN-α” and “IFN-γ”; and granulocyte macrophage colony stimulating factor, “GM-CSF”), or that attempt to provoke a tumor-specific immune response to certain tumor antigens, such as dendritic cell vaccines and antibodies against specific tumor antigens and even adoptive T-cell therapy. Additional approaches have attempted to elicit systemic response following repeated inoculation of tumors with certain immunostimulatory agents, such as an intralesional vaccine containing an oncolytic herpes virus encoding GM-CSF or a plasmid encoding human leukocyte antigen-B7 and beta-2 microglobulin agent designed to express allogeneic major histocompatibility complex (MHC) class I antigens. For various reasons including, but not limited to, potential systemic toxicity of these immunomodulating agents, differential expression of the targeted moieties or responsiveness of clonal subpopulations, increase of tumor burden during therapy induction, and development of resistance against the selected mode of attack, current regimens may not result in as robust an immune response as desired, again allowing considerable room for improvement in terms of efficacy and safety.
Combination of systemic immunomodulatory agents with systemic chemotherapy agents or kinase inhibitors has been proposed, for example by Jure-Kunkel and Lee (WO 2010/014784), however there is limited data to determine whether such an approach will be clinically significant. In principal, this approach combines the features of targeted therapy (using chemotherapy or a metabolic inhibitor) with immunomodulation in a combination therapy, and as is the case with standard chemotherapeutic combination therapy it provides a means to attack cancer simultaneously via several different paths, thereby increasing potency while reducing likelihood of resistance. Since the immunologic consequences of chemotherapy may at least partially counteract the activity of the immunomodulator, and their respective systemic adverse effects may be additive or synergistic, such a combination of modalities has significant potential shortcomings. While not the topic of Jure-Kunkel and Lee, targeted therapies when combined with immunomodulatory agents can also have these negative effects. Perhaps most importantly, these potential combinations don't appear to afford additive or synergistic tumoricidal potency in terms of immunologic benefit since neither chemotherapy nor metabolic or aberrant gene targeting can be expected to significantly activate an antitumor immune response, while the proposed anti-CTLA-4 targeting is similarly unlikely to increase sensitivity of tumor cells to the companion chemotherapy or tumor specific approach. The possibility of increased tumor burden during induction of immunomodulatory therapy further complicates the picture, raising the possibility that the disease may progress to an unacceptably advanced state during the early phases of the regimen.
Further complicating the therapeutic challenge, tumors that shrink gradually over a long period of time and slowly release immunoreactive tumor materials in response to any of these conventional systemic therapies may fail to trigger a potent protective response and can instead facilitate reduced antitumor immunity. This phenomenon is similar to that underlying low dose therapies for allergies whereby the host is repeatedly exposed to low doses of antigenic material over a prolonged period, eliciting tolerance by causing the immune system to identify these persistent “background” antigens as “self” (i.e., a normal part of the host). In a similar fashion, the slow, low dose release of tumor antigens to the immune system in response to many systemic therapies may deceive the immune system into tolerance toward tumor antigens thereby reducing or negating possible antitumor response, potentially prolonging tumor survival, and allowing continued metastatic spread.
An alternate class of therapies is predicated on physical restriction of delivery of the therapeutic modality to diseased tissue. These localized therapies attempt to maximize potency of the therapy within tumor tissue while reducing systemic exposure. Approaches include physical or chemical disruption of tumors using intralesional methods, such as percutaneous ethanol injection therapy (PEIT) and radiofrequency (RF) ablation, and locoregional delivery of potent cytotoxic agents, such as isolated limb perfusion (ILP), isolated limb infusion (ILI) or percutaneous hepatic perfusion (PHP), with melphalan (an alkylating agent) or similar agents. While these approaches are often quite effective in maximizing pharmacologic activity against the treated tumor, they have generally exhibited many of the same limitations of systemic therapies due to the inherent shortcomings of the underlying therapeutic modality, including limited specificity for the targeted cancer with significant locoregional toxicity, and minimal impact on systemic disease, particularly for those approaches having no mechanism for immune stimulation against the treated tumor.
The use of cancer-specific cytotoxic agents delivered via an intralesional (IL) route (i.e., IL chemoablation) is a novel hybrid approach that has been described by one or more of the present inventors (for example in U.S. Pat. No. 7,648,695, U.S. Ser. No. 11/951,800 and U.S. Ser. No. 12/315,781, which are incorporated herein in their entirety). This approach maximizes local efficacy against injected tumors while minimizing systemic exposure of the patient to the injected agent and resultant potential for systemic adverse effects. One or more of the present inventors have shown that IL use of a certain specific class of agent (for example certain formulations of certain halogenated xanthenes, exemplified by a 10% (w/v) solution of rose bengal disodium in saline, termed “PV-10” and undergoing clinical testing for treatment of metastatic melanoma, breast carcinoma and hepatocellular carcinoma) can elicit not only highly specific ablation of the injected lesion but also an antitumor immune response (“bystander effect”) that can augment local efficacy in the injected tumor and lead to spontaneous regression of uninjected tumors. Nonclinical evidence indicates that high levels of granulocytes (such as basophils, eosinophils and mast cells) may be expressed in the tissue surrounding tumors, indicating that the host is attempting to mount a non-specific immune response to tumor tissue. Treatment of tumors with PV-10 can lead to modulation of this response to one that is more specific and effective (for example, by recruiting mononuclear tumor-infiltrating lymphocytes, TILs, or macrophages into and around the tumor). It is likely that acute tumor disruption resulting from IL chemoablation with PV-10 releases sequestered, intact tumor antigens to local antigen-presenting cells (APCs), facilitating modulation of the immune response and presentation of appropriate antigenic targets to T and B-cells. Collateral destruction of granulocytes surrounding the tumor may precipitate chemokine release and local inflammation, and may serve an adjuvant role in promoting specific antitumor response. In situ destruction of the injected tumor assures presentation of tumor antigens in their natural context, thereby maximizing potential response of the immune system to the treated tumor and to tumors bearing the same immunologic signature. Since immune response is proportional to the intensity and duration of the insult to the host, the acute exposure achieved through IL chemoablation is immunologically advantageous relative to the lesser intensity insult produced by a systemic therapy that is spread out over a long duration, and this acute exposure potentially vaccinates the patient against the treated tumor.
Acute ablation of the injected tumor also quickly reduces tumor burden, which may be augmented by injecting all or a substantial fraction of a patient's tumors, either in a single treatment session or a series of treatments fractionated over a period of days or weeks. This may reduce the level of immune suppression exerted by the patient's tumor mass, leading to improved ability of their immune system to mount a successful attack against remaining tumor tissue. The inherent suitability of IL chemoablation for use against large or multiple cancerous lesions, when present, may further enhance outcome by facilitating in situ inoculation against potentially distinct clonal subpopulations in different tumors (or even within individual tumors) that may arise during tumor growth and metastasis.
While IL chemoablation overcomes many of the shortcomings of prior therapeutic modalities (for example by achieving rapid reduction in tumor burden, maximizing acute exposure to intact tumor antigens in an appropriate context, and affording minimal potential for systemic adverse effects) one or more of the present inventors have found that it may not be ideal for all cancer cases, particularly certain advanced cases having rapidly proliferating tumors, those with widely disseminated disease and those that present in forms that are difficult to fully infiltrate with the IL agent. Accordingly, additional advancements are needed in the fields of oncology and improved therapeutic regimens therefore.